This invention relates to a gas turbine engine component. In particular, the invention relates to fastening of load carrying composite vanes to a ring element. The invention also relates to a gas turbine engine comprising such a component.
Turbojet engines often comprise a fan part with a gas/air channel defined by an outer ring (outer casing) and an inner ring (inner casing) connected by a plurality of air-guiding vanes and structural, load-carrying vanes that extend in a radial direction between the two rings. An engine mount is usually also provided by means of which the engine can be suspended in a frame, such as a wing of an aircraft. The engine mount is commonly attached to the above-mentioned outer ring. A structure of the type described above will be subjected to large mechanical forces upon operation of the engine and must be designed to withstand such conditions.
Conventionally, the vanes and the ring elements have been made of metal and fastening of the vanes to the ring elements has been achieved by means of bolt or rivet friction joints. However, for the purpose of saving weight there is an increasing interest of making use of vanes and ring elements made of a composite material such as a fibre-reinforced polymer.
Fastening of composite components is generally more complex than fastening of metal components. One reason is that composite materials have a tendency to relax mechanically during its lifetime, which results in that an initially applied clamping friction force is likely to decrease with time. Another reason is that a fibre-reinforced composite material usually exhibits different mechanical properties in different directions, which requires certain considerations regarding the transmission of forces through the fastening arrangement. Conventional friction joints are therefore normally not suitable for fastening e.g. a load-carrying composite vane to a ring element.
WO 2008/121047 discloses an arrangement for fastening a load carrying composite vane to a ring element using a ring element stiffening structure and a bracket member, wherein particular attention is paid to the subject of direction of forces.
There is still a need for improvements in this field, for instance regarding the problem related to the tendency of composite materials to relax mechanically during its lifetime.
It is desirable to provide a gas turbine engine component and gas turbine engine that exhibit improved properties concerning fastening of composite load-carrying vanes to a ring element compared to conventional gas turbine engines and components.
The invention concerns, according to an aspect thereof, a gas turbine engine component comprising: a ring element and a plurality of circumferentially spaced load carrying vanes extending in a radial direction of the ring element; wherein at least one of said vanes is made of a composite material, and wherein the at least one composite vane is fastened to the ring element, said component further comprising: first and second wall portions that are fixed in relation to the ring element and arranged on opposite sides of the composite vane; and at least a first hole extending through the first wall portion, the composite vane and the second wall portion, wherein said first hole is adapted to receive a first insertion member.
An aspect of the invention is characterized in that that the component is arranged such as to, with regard to the first hole, provide a tight fit for the first insertion member in the first wall portion as well as in the composite vane and to provide a loose fit with a radial play in the second wall portion.
In an aspect of the inventive design the tight fitting achieved between an insertion member, such as a bushing or a bolt, positioned in the first hole provides a fixed position of the vane in relation to the first wall portion. Thereby a rigid load path is provided without having to apply large clamping forces. A rigid load path is important for avoiding a gap/play that may result in sliding and reduced stiffness that limits the functionality during operation of engine. Moreover, tolerances can be taken up by the loose fit radial play in the second wall portion. Thus, tolerances can be taken up by adjusting the relative position of the wall portions. This is useful when providing a corresponding fixed position of the vane in relation to the second wall portion (for instance by a tight fit arrangement as described above) and when fastening the vane and wall portions to the ring element.
A known way of achieving a tight fit between a bolt or other insertion member and a hole that extends through a plurality of parts to be joined is line drilling, i.e. the parts to be joined are drilled through jointly in one operation. However, such line drilling has drawbacks in that it is relatively time-consuming and thereby costly, in that the parts will be unique and generally not replaceable and further in that the machining operation may be complex in case one part is in metal and another in composite material. In the inventive design a tight fit is provided without line drilling.
The terms tight fit and loose fit are well recognized terms for a person skilled in the art. A tight fit means that the hole has the same size (diameter) or is only slightly larger than the insertion member, in this case with a radial play of <0.1 mm and typically 0.015-0.1 mm. A loose fit means enough clearance to allow free play at any tolerance condition expected for the particular parts to be joined. Loose fit means in this case that the radial play to the insertion member is >0.3 mm and typically 0.4-0.6 mm.
In an advantageous embodiment of the invention the component comprises a second hole extending through the first wall portion, the composite vane and the second wall portion, wherein said second hole is adapted to receive a second insertion member, said first and second holes being positioned at a distance from each other as seen in an axial direction of the ring element, wherein the component further being arranged such as to, with regard to the second hole, provide a tight fit for the second insertion member in the second wall portion as well as in the composite vane and to provide a loose fit with a radial play in the first wall portion.
Thus, in this embodiment the insertion member in the second hole has a cross-wise opposite tight fit-loose fit as compared to the insertion member in the first hole. The tight fittings provide in this case a fixed position of the vane in relation to both the first and the second wall portions (without having to drill jointly). Tolerances can be taken up by the loose fittings in both wall portions which means that, if so required, the relative position of the two wall portions can be adjusted to allow insertion of both the first and second insertion member into the first and second holes, respectively. Further, a fastening arrangement comprising two holes and two corresponding insertion members, where the holes are positioned at a distance from each other as seen in an axial direction of the ring element, is well adapted to secure the vane to the ring element.
In a further embodiment of the invention the fastening arrangement is configured to allow adjustment of the relative positions of the first and second wall portions. Preferably, at least one of the wall portions forms part of a separate bracket member that is fastened to the ring element and to the composite vane. Such a separate bracket member can be easily be position-adjusted and fastened when assembling the component. Preferably, the separate bracket member is fastened to the ring element by means of a fastening device that allows its position to be adjusted. Such an arrangement can e.g. include bolt holes with sufficient tolerances and/or shims for adjusting the distance between bracket member and its point of attachment at the ring element
In a further embodiment of the invention the first insertion member extends in the first hole along an axial direction thereof. In one embodiment the first insertion member is a bushing member. Preferably, the component comprises a fastening member that extends in an axial direction through the first hole, wherein the bushing member extends at least partly around and along the fastening member. In another embodiment the first insertion member is an elongated fastening member, such as a bolt or a rivet.
In a further embodiment of the invention a third hole is arranged in-between the first and second holes, wherein said third hole is adapted to receive a third insertion member, and wherein the component is arranged such as to, with regard to the third hole, provide a loose fit with a radial play for the third insertion member in the first and the second wall portions and to provide a tight fit in the in the composite vane. Such a design is useful for reducing vibrations.
In a further embodiment of the invention the component comprises an inner ring element and an outer ring element connected by said plurality of circumferentially spaced load carrying vanes.
In a further embodiment of the invention the component is configured to define a gas flow in a gas turbine engine, such as a turbo jet engine.
In a further embodiment of the invention the first and second wall portions are made of a metallic material.
The invention also concerns, according to another aspect thereof, a gas turbine engine comprising a gas turbine engine component of the above type.